Ink, ink container, and inkjet recording apparatus

ABSTRACT

An ink including an organic solvent, a pigment, a polyurethane particle, and water is provided. The organic solvent includes at least one of 3-methoxy-1-butanol and 3-methoxy-1-propanol. The polyurethane particle has a particle diameter D50 of 50 nm or less.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35U.S.C. § 119(a) to Japanese Patent Application Nos. 2015-147564 and2015-178241, filed on Jul. 27, 2015, and Sep. 10, 2015, respectively, inthe Japan Patent Office, the entire disclosure of each of which ishereby incorporated by reference herein.

BACKGROUND

Technical Field

The present disclosure relates to an ink, an ink container, and aninkjet recording apparatus.

Description of the Related Art

Inkjet recording process is generally simpler than other recordingprocesses. It is generally easy to provide a simple high-resolutionfull-color image forming apparatus employing inkjet recording process.As inks used for inkjet recording process (hereinafter “inkjet inks”),dye inks are widely used, in which a water-soluble dye is dissolved inwater or a mixture liquid of water and a water-soluble humectant.

On the other hand, aqueous pigment inks (hereinafter simply “pigmentinks”) in which fine particles of a water-dispersible pigment aredispersed in water are attracting attention, in accordance withincreasing needs of high-speed image forming apparatuses. It is knownthat such inkjet inks using a water-dispersible pigment have excellentwater resistance and light resistance. However, when an image isrecorded with such a pigment ink on glossy paper, the pigment in the inkremains on the surface of the glossy paper forming its film withoutpermeating the ink receiving layer of the glossy paper. The image thusrecorded with a pigment ink on glossy paper is generally inferior interms of rub resistance than that recorded with a pigment ink on plainpaper or with a dye ink that can permeate the ink receiving layer. Asthe image recorded with a pigment ink on glossy paper is rubbed, the inkfilm will be peeled off and stretched over non-printed parts and therubbed surface will be fouled.

SUMMARY

In accordance with some embodiments of the present invention, an ink isprovided. The ink includes an organic solvent, a pigment, a polyurethaneparticle, and water. The organic solvent includes at least one of3-methoxy-1-butanol and 3-methoxy-1-propanol. The polyurethane particlehas a particle diameter D50 of 50 nm or less.

In accordance with some embodiments of the present invention, an inkcontainer is provided. The ink container includes a container and theabove ink contained in the container.

In accordance with some embodiments of the present invention, an inkjetrecording apparatus is provided. The inkjet recording apparatus includesthe above ink container and a recording head to discharge the ink.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view of an ink bag according to an embodiment ofthe present invention;

FIG. 2 is a schematic view of an ink cartridge according to anembodiment of the present invention, storing the ink bag illustrated inFIG. 1;

FIG. 3 is a perspective view of an inkjet recording apparatus accordingto an embodiment of the present invention;

FIG. 4 is a cross-sectional view of the inkjet recording apparatusillustrated in FIG. 3; and

FIG. 5 is a partial cross-sectional view of the inkjet recordingapparatus illustrated in FIG. 3.

The accompanying drawings are intended to depict example embodiments ofthe present invention and should not be interpreted to limit the scopethereof. The accompanying drawings are not to be considered as drawn toscale unless explicitly noted.

DETAILED DESCRIPTION

Embodiments of the present invention are described in detail below withreference to accompanying drawings. In describing embodimentsillustrated in the drawings, specific terminology is employed for thesake of clarity. However, the disclosure of this patent specification isnot intended to be limited to the specific terminology so selected, andit is to be understood that each specific element includes all technicalequivalents that operate in a similar manner and achieve a similarresult.

For the sake of simplicity, the same reference number will be given toidentical constituent elements such as parts and materials having thesame functions and redundant descriptions thereof omitted unlessotherwise stated.

In accordance with some embodiments of the present invention, an inkhaving improved rub resistance and excellent storage stability isprovided.

An ink according to an embodiment of the present invention includes anorganic solvent, a pigment, a polyurethane particle, and water. Theorganic solvent includes at least one of 3-methoxy-1-butanol and3-methoxy-1-propanol. The polyurethane particle has a particle diameterD50 of 50 nm or less.

The combined use of the pigment and the polyurethane particle having aparticle diameter D50 of 50 nm or less improves rub resistance of animage formed with the ink. The polyurethane particle having a smallparticle diameter acts as an adhesive between the pigment particles.Thus, in the image formed with the ink on a medium, the pigmentparticles are less likely to release from the medium even when beingrubbed.

The particle diameter D50 of the polyurethane particle can be measuredwith, for example, a particle size distribution analyzer (NANOTRACUPA-EX150 available from Nikkiso Co., Ltd.).

It is known that an ink including a polyurethane particle is likely toexpress a lower viscosity when stored. Specifically, when thepolyurethane particle in the ink has a particle diameter D50 of 30 nm orless, the degree of viscosity decrease becomes much greater. A possiblereason for this phenomenon is that as the specific surface area of thepolyurethane particle becomes large, the polyurethane particle becomesmore frequently attacked by the solvent. In particular, when theparticle diameter D50 is 10 nm or less, the polyurethane particle willbe dissolved in the solvent and no more exist in the form of a particle.The dissolved polyurethane will flow on the medium along with thesolvent without improving fixing strength of the image. The dissolvedpolyurethane also increases the viscosity of the solvent in a rapidmanner, thus increasing the initial viscosity of the ink.

The inventors of the present invention have found that the viscositydecrease of the conventional ink occurs when the ink is stored becausethe organic solvent gradually comes into between the polyurethanemolecules. The inventors of the present invention have also found thatwhen the organic solvent includes at least one of 3-methoxy-1-butanoland 3-methoxy-1-propanol, the organic solvent can come into between thepolyurethane resin molecules in a shorter time, thus bringing the inkinto a stable state without causing viscosity decrease or increase.

Preferably, 3-methoxy-1-butanol and/or 3-methoxy-1-propanol account(s)for 0.8% to 12% by mass of the ink, more preferably, 2% to 9% by mass ofthe ink. When the content rate of 3-methoxy-1-butanol and/or3-methoxy-1-propanol in the ink ranges from 0.8% to 12% by mass, theoccurrence of viscosity decrease is sufficiently suppressed when the inkis stored.

In a case in which 3-methoxy-1-butanol and 3-methoxy-1-propanol are usedin combination, the total content rate thereof preferably ranges from0.8% to 12% by mass.

In addition, it is preferable that the mass ratio of the3-methoxy-1-butanol and/or 3-methoxy-1-propanol to the polyurethaneparticle ranges from 0.2 to 5.0. When the mass ratio is in the range offrom 0.2 to 5.0, the ink expresses good discharge stability. It is morepreferable that the mass ratio of the 3-methoxy-1-butanol and/or3-methoxy-1-propanol to the polyurethane particle ranges from 0.5 to 4.

The polyurethane particle has a particle diameter D50 of 50 nm or less,as described above. More preferably, the polyurethane particle has aparticle diameter D50 of from 10 to 30 nm.

Ink

Compositional materials of the ink (e.g., organic solvent, water,pigment, resin, other additives) are described in detail below.

Organic Solvent

In accordance with some embodiments of the present invention, theorganic solvent includes at least one of 3-methoxy-1-butanol and3-methoxy-1-propanol. In addition to 3-methoxy-1-butanol and/or3-methoxy-1-propanol, the ink may further include another water-solubleorganic solvent. Usable water-soluble organic solvents include polyols,ethers (e.g., polyol alkyl ethers, polyol aryl ethers),nitrogen-containing heterocyclic compounds, amides, amines, andsulfur-containing compounds.

Specific examples of the water-soluble organic solvents include, but arenot limited to, polyols (e.g., ethylene glycol, diethylene glycol,1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol,1,4-butanediol, 2,3-butanediol, 3-methyl-1,3-butanediol, triethyleneglycol, polyethylene glycol, polypropylene glycol, 1,2-pentanediol,1,3-pentanediol, 1,4-pentanediol, 2,4-pentanediol, 1,5-pentanediol,1,2-hexanediol, 1,6-hexanediol, 1,3-hexanediol, 2,5-hexanediol,1,5-hexanediol, glycerin, 1,2,6-hexanetriol, 2-ethyl-1,3-hexanediol,ethyl-1,2,4-butanetriol, 1,2,3-butanetriol,2,2,4-trimethyl-1,3-pentanediol, 3-methyl-1,3,5-pentanetriol), polyolalkyl ethers (e.g., ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycolmonomethyl ether, propylene glycol monoethyl ether), polyol aryl ethers(e.g., ethylene glycol monophenyl ether, ethylene glycol monobenzylether), nitrogen-containing heterocyclic compounds (e.g., 2-pyrrolidone,N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone,1,3-dimethyl-2-imidazolidinone, ε-caprolactam, γ-butyrolactone), amides(e.g., formamide, N-methylformamide, N,N-dimethylformamide,3-methoxy-N,N-dimethyl propionamide, 3-butoxy-N,N-dimethylpropionamide),amines (e.g., monoethanolamine, diethanolamine, triethylamine),sulfur-containing compounds (e.g., dimethylsulfoxide, sulfolane,thiodiethanol), propylene carbonates, and ethylene carbonates.

Organic solvents having a boiling point of 250° C. or less arepreferable since they function as a wetting agent while providing gooddrying property.

In addition, polyol compounds having 8 or more carbon atoms and glycolether compounds are also preferable. Specific examples of polyolcompounds having 8 or more carbon atoms include, but are not limited to,2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

Specific examples of glycol ether compounds include, but are not limitedto, polyol alkyl ethers (e.g., ethylene glycol monoethyl ether, ethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, diethyleneglycol monoethyl ether, diethylene glycol monobutyl ether, tetraethyleneglycol monomethyl ether, propylene glycol monoethyl ether) and polyolaryl ethers (e.g., ethylene glycol monophenyl ether, ethylene glycolmonobenzyl ether).

The polyol compounds having 8 or more carbon atoms and the glycol ethercompounds are capable of improving paper-permeability of the ink, whichis advantageous when the ink is printed on a recording medium made ofpaper.

The content rate of the organic solvent in the ink is preferably in therange of from 10% to 60% by mass, more preferably from 20% to 60% bymass, from the aspects of ink drying property and discharge reliability,but is not limited thereto.

Water

The content rate of the water in the ink is preferably in the range offrom 10% to 90% by mass, more preferably from 20% to 60% by mass, fromthe aspects of ink drying property and discharge reliability, but is notlimited thereto.

Pigment

Usable pigments include both inorganic pigments and organic pigments.One pigment can be used alone, or two or more pigments can be used incombination. Mixed crystal pigments can also be used.

Usable pigments include black pigments, yellow pigments, magentapigments, cyan pigments, white pigments, green pigments, orangepigments, glossy color pigments (e.g., gold pigments, silver pigments),and metallic pigments.

Specific examples of inorganic pigments include, but are not limited to,titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminumhydroxide, barium yellow, cadmium red, chrome yellow, and carbon blackproduced by a known method, such as a contact method, a furnace method,and a thermal method.

Specific examples of organic pigments include, but are not limited to,azo pigments, polycyclic pigments (e.g., phthalocyanine pigments,perylene pigments, perinone pigments, anthraquinone pigments,quinacridone pigments, dioxazine pigments, indigo pigments, thioindigopigments, isoindolinone pigments, quinophthalone pigments), dye chelates(e.g., basic dye chelate, acid dye chelate), nitro pigments, nitrosopigments, and aniline black. Among these pigments, those having goodaffinity for solvents are preferable. In addition, resin hollowparticles and inorganic hollow particles can also be used.

Specific examples of pigments used for black-and-white printing include,but are not limited to: carbon blacks (i.e., C.I. Pigment Black 7) suchas furnace black, lamp black, acetylene black, and channel black; metalssuch as copper, iron (i.e., C.I. Pigment Black 11), and titanium oxide;and organic pigments such as aniline black (i.e., C.I. Pigment Black 1).

Specific examples of pigments used for color printing include, but arenot limited to: C.I. Pigment Yellow 1, 3, 12, 13, 14, 17, 24, 34, 35,37, 42 (yellow iron oxide), 53, 55, 74, 81, 83, 95, 97, 98, 100, 101,104, 108, 109, 110, 117, 120, 138, 150, 153, 155, 180, 185, and 213;C.I. Pigment Orange 5, 13, 16, 17, 36, 43, and 51; C.I. Pigment Red 1,2, 3, 5, 17, 22, 23, 31, 38, 48:2, 48:2 (Permanent Red 2B(Ca)), 48:3,48:4, 49:1, 52:2, 53:1, 57:1 (Brilliant Caunine 6B), 60:1, 63:1, 63:2,64:1, 81, 83, 88, 101 (red iron oxide), 104, 105, 106, 108(cadmium red),112, 114, 122 (quinacridone magenta), 123, 146, 149, 166, 168, 170, 172,177, 178, 179, 184, 185, 190, 193, 202, 207, 208, 209, 213, 219, 224,254, and 264; C.I. Pigment Violet 1 (rhodamine lake), 3, 5:1, 16, 19,23, and 38; C.I. Pigment Blue 1,2,15 (phthalocyanine blue), 15:1, 15:2,15:3, 15:4 (phthalocyanine blue), 16, 17:1, 56, 60, and 63; and C.I.Pigment Green 1,4,7,8,10,17,18, and 36.

The content rate of the pigment in the ink is preferably in the range offrom 0.1% to 15% by mass, more preferably from 1% to 10% by mass, fromthe aspects of image density, fixing strength, and discharge stability.

The pigment can be dispersed in the ink by one of the following methods:a first method in which a hydrophilic functional group is introduced tothe pigment to make the pigment self-dispersible; a second method inwhich the surface of the pigment gets covered with a resin; and a thirdmethod in which the pigment gets dispersed by a dispersant.

In the first method, for example, a functional group such as sulfonegroup and carboxyl group may be introduced to the pigment (e.g., carbonblack) to make the pigment self-dispersible in water.

In the second method, for example, the pigment may get incorporated in amicrocapsule so that the pigment becomes self-dispersible in water. Inthis case, the pigment may be restated as a resin-covered pigment. Notall the pigment particles included in the ink should be covered with aresin. It is possible that a part of the pigment particles are notcovered with any resin or partially covered with a resin.

In the third method, for example, low-molecular dispersants andhigh-molecular dispersants, represented by known surfactants, may beused.

More specifically, any of anionic surfactants, cationic surfactants,ampholytic surfactants, and nonionic surfactants may be selecteddepending on the property of the pigment.

For example, a nonionic surfactant RT-100 (product of Takemoto Oil & FatCo., Ltd.) and sodium naphthalenesulfonate formalin condensate arepreferably used as the dispersant. One dispersant can be used alone, andtwo or more dispersants can be used in combination.

Pigment Dispersion

The ink can be obtained by mixing the pigment with other materials suchas water and the organic solvent. The ink can also be obtained by,preparing a pigment dispersion by mixing the pigment with water, apigment dispersant, etc. first, and then mixing the pigment dispersionwith other materials such as water and the organic solvent.

The pigment dispersion includes water, the pigment, the pigmentdispersant, and other components, if any. The pigment is dispersed inthe pigment dispersion with the adjusted particle diameter. The pigmentdispersion is preferably prepared using a disperser.

Preferably, the pigment dispersed in the pigment dispersion has amaximum frequency particle diameter in the range of from 200 to 500 nm,more preferably from 20 to 150 nm, based on the number of pigmentparticles, from the aspects of dispersion stability of the pigment anddischarge stability and image quality (e.g., image density) of the ink.The particle diameter of the pigment can be measured with, for example,a particle size distribution analyzer (NANOTRAC WAVE-UT151 availablefrom MicrotracBEL Corp.).

The content rate of the pigment in the pigment dispersion is preferablyin the range of from 0.1% to 50% by mass, more preferably from 0.1% to30% by mass, from the aspects of discharge stability and image density,but is not limited thereto.

The pigment dispersion may be preferably subjected to filtration using afilter or a centrifugal separator to remove coarse particles and thendegassing.

Polyurethane Particle

The ink includes a polyurethane particle for the purpose of improvingrub resistance of the resulting image and storage stability of the inkcontaining the pigment.

The polyurethane is obtainable by polymerizing a polyisocyanate with apolyether polyol, a polyester polyol, a polylactone polyol, and/or apolycarbonate polyol. Specific examples of the polyisocyanate include,but are not limited to, aliphatic diisocyanate compounds (e.g.,hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate),alicyclic diisocyanate compounds (e.g., isophorone diisocyanate,hydrogenated xylylene diisocyanate, 1,4-cyclohexane diisocyanate,4,4′-dicyclohexylmethane diisocyanate), aromatic aliphatic diisocyanatecompounds (e.g., xylylene diisocyanate, tetramethylxylylenediisocyanate), aromatic diisocyanate compounds (e.g., tolylenediisocyanate, phenylmethane diisocyanate), and modified products ofthese diisocyanate compounds (e.g., carbodiimide, uretdione,uretonimine-containing modified products.)

Specific examples of the polyether polyol include, but are not limitedto, polyethylene glycol, polypropylene glycol, polytetramethylene etherglycol, and polyhexamethylene ether glycol.

Specific examples of the polyester polyol include, but are not limitedto, polyethylene adipate, polybutylene adipate, polyneopentyl adipate,poly-3-methylpentyl adipate, polyethylene/butylene adipate,polyneopentyl/hexyl adipate.

Specific examples of the polylactone polyol include, but are not limitedto, polycaprolactone diol, poly-omega-hydroxycaproic acid polyol.

Specific examples of the polycarbonate polyol include, but are notlimited to, reaction products of diols (e.g., propanediol-(1,3),butanediol-(1,4), hexanediol-(1,6), diethylene glycol, triethyleneglycol, tetraethylene glycol), phosgene, and diaryl carbonates (e.g.,diphenyl carbonate) or cyclic carbonates (e.g., ethylene carbonate,propylene carbonate).

The content rate of the polyurethane particle in the ink is preferablyin the range of from 0.5% to 5% by mass, more preferably from 1% to 3%by mass, from the aspects of fixing strength and ink storage stability,but is not limited thereto.

The polyurethane resin can express much improved water dispersibility inan emulsion as an ionic group is introduced thereto. Specific examplesof the ionic group include, but are not limited to: sulfonic acid group,carboxylic acid group, sulfuric acid group, phosphonic acid group, andphosphinic acid group; and alkali metal salt group, alkali earth metalsalt group, ammonium salt group, and first to third amine group of theabove acids. In particular, carboxylic acid alkali metal salt group,carboxylic acid ammonium salt group, sulfonic acid alkali metal saltgroup, and sulfonic acid ammonium salt group are preferable. From theaspect of water dispersion stability, sulfonic acid alkali metal saltgroup and sulfonic acid ammonium salt group are preferable. Introductionof the ionic group to the resin may be performed by adding a monomerhaving the ionic group at the time when the resin is being synthesized.The metal salt is preferably Li, K, or Na salt.

Surfactant

Usable surfactants include silicone-based surfactants, fluorine-basedsurfactants, ampholytic surfactants, nonionic surfactants, and anionicsurfactants.

Specific examples of the silicone-based surfactants include thoseindecomposable at high pH, such as side-chain-modifiedpolydimethylsiloxane, both-terminals-modified polydimethylsiloxane,one-terminal-modified polydimethylsiloxane, andside-chain-and-both-terminals-modified polydimethylsiloxane. Morespecifically, those having polyoxyethylene group and/or polyoxyethylenepolyoxypropylene group as the modifying group are more preferable sincethey exhibit good properties as an aqueous surfactant. Specific examplesof the silicone-based surfactants further include polyether-modifiedsilicone-based surfactants, such as a dimethyl siloxane having apolyalkylene oxide structure on its side chain bonded to Si atom.

Specific examples of the fluorine-based surfactants include, but are notlimited to, perfluoroalkyl sulfonic acid compounds, perfluoroalkylcarboxylic acid compounds, perfluoroalkyl phosphate compounds,perfluoroalkyl ethylene oxide adducts, and polyoxyalkylene ether polymercompounds having a perfluoroalkyl ether group on its side chain, whichhave weak foaming property. Specific examples of the perfluoroalkylsulfonic acid compounds include, but are not limited to, perfluoroalkylsulfonic acid and perfluoroalkyl sulfonate. Specific examples of theperfluoroalkyl carboxylic acid compounds include, but are not limitedto, perfluoroalkyl carboxylic acid and perfluoroalkyl carboxylate.Specific examples of the polyoxyalkylene ether polymer compounds havinga perfluoroalkyl ether group on a side chain include, but are notlimited to, a sulfate of a polyoxyalkylene ether polymer having aperfluoroalkyl ether group on its side chain, and a salt of apolyoxyalkylene ether polymer having a perfluoroalkyl ether group on itsside chain. Specific examples of the counter ions for thesefluorine-based surfactants include, but are not limited to, Li, Na, K,NH₄, NH₃CH₂CH₂OH, NH₂(CH₂CH₂OH)₂, and NH(CH₂CH₂OH)₃.

Specific examples of the ampholytic surfactants include, but are notlimited to, laurylaminopropionate, lauryl dimethyl betaine, stearyldimethyl betaine, and lauryl hydroxyethyl betaine.

Specific examples of the nonionic surfactants include, but are notlimited to, polyoxyethylene alkyl phenyl ethers, polyoxyethylene alkylesters, polyoxyethylene alkyl amines, polyoxyethylene alkyl amides,polyoxyethylene propylene block copolymers, sorbitan fatty acid esters,polyoxyethylene sorbitan fatty acid esters, and ethylene oxide adductsof acetylene alcohol.

Specific examples of the anionic surfactants include, but are notlimited to, acetate, dodecylbenzene sulfonate, and laurate ofpolyoxyethylene alkyl ether, and polyoxyethylene alkyl ether sulfate.

Each of these compounds can be used alone or in combination with others.

Specific examples of the silicone-based surfactants include, but are notlimited to, side-chain-modified polydimethylsiloxane,both-terminals-modified polydimethylsiloxane, one-terminal-modifiedpolydimethylsiloxane, and side-chain-and-both-terminals-modifiedpolydimethylsiloxane. More specifically, polyether-modifiedsilicone-based surfactants having polyoxyethylene group and/orpolyoxyethylene polyoxypropylene group as the modifying groups arepreferable since they exhibit good properties as an aqueous surfactant.

These surfactants are available either synthetically or commercially.Commercial products are readily available from BYK Japan KK, Shin-EtsuChemical Co., Ltd., Dow Corning Toray Co., Ltd., Nihon Emulsion Co.,Ltd., and Kyoeisha Chemical Co., Ltd. Specific examples of thepolyether-modified silicone-based surfactants include, but are notlimited to, a compound represented by the following formula (S-1) thatis a dimethylpolysiloxane having a polyalkylene oxide structure on itsside chain bonded to Si atom.

In the formula (S-1), each of m, n, a, and b independently represents aninteger, and R and R′ independently represents an alkyl group or analkylene group.

Specific examples of commercially-available polyether-modifiedsilicone-based surfactants include, but are not limited to: KF-618,KF-642, and KF-643 (available from Shin-Etsu Chemical Co., Ltd.);EMALEX-SS-5602 and SS-1906EX (available from Nihon Emulsion Co., Ltd.);FZ-2105, FZ-2118, FZ-2154, FZ-2161, FZ-2162, FZ-2163, and FZ-2164(available from Dow Corning Toray Co., Ltd; BYK-33 and BYK-387(available from BYK Japan KK); and TSF4440, TSF4452, and TSF4453(available from Momentive Performance Materials Inc.).

Preferably, the fluorine-based surfactant is a compound having 2 to 16fluorine-substituted carbon atoms, more preferably a compound having 4to 16 fluorine-substituted carbon atoms.

Specific examples of the fluorine-based surfactants include, but are notlimited to, perfluoroalkyl phosphate compounds, perfluoroalkyl ethyleneoxide adducts, and polyoxyalkylene ether polymer compounds having aperfluoroalkyl ether group on its side chain. Among these fluorine-basedsurfactants, polyoxyalkylene ether polymer compounds having aperfluoroalkyl ether group on its side chain is preferable since foamingproperty thereof is small. More specifically, compounds represented bythe following formula (F-1) and (F-2) are preferable.CF₃CF₂(CF₂CF₂)_(m)—CH₂CH₂O(CH₂CH₂O)_(n)H  (F-1)

In the formula (F-1), to have water-solubility, m is preferably aninteger of from 0 to 10, and n is preferably an integer of from 0 to 40.C_(n)F_(2n+1)—CH₂CH(OH)CH₂—O—(CH₂CH₂O)_(a)—Y  (F-2)

In the formula (F-2), Y represents H, C_(n)F_(2n+1) (wherein nrepresents an integer of from 1 to 6), CH₂CH(OH)CH₂—C_(n)F_(2n+1)(wherein n represents an integer of from 4 to 6), or C_(p)F_(2p+1)(wherein p represents an integer of from 1 to 19 and n represents aninteger of from 1 to 6); and a represents an integer of from 4 to 14.

The fluorine-based surfactants are available either synthetically orcommercially.

Specific examples of commercially-available fluorine-based surfactantsinclude, but are not limited to: SURFLON S-111, S-112, S-113, S-121,S-131, S-132, S-141, and S-145 (available from AGC Seimi Chemical Co.,Ltd.); Fluorad™ FC-93, FC-95, FC-98, FC-129, FC-135, FC-170C, FC-430,and FC-431 (available from 3M); MEGAFACE F-470, F-1405, and F-474(available from DIC Corporation); Zonyl® TBS, FSP, FSA, FSN-100, FSN,FSO-100, FSO, FS-300, and UR (available from E. I. du Pont de Nemoursand Company); FT-110, FT-250, FT-251, FT-400S, FT-150, and FT-400SW(available from NEOS COMPANY LIMITED); PolyFox PF-136A, PF-156A,PF-151N, PF-154, and PF-159 (available from OMNOVA Solutions Inc.); andUNIDYNE™ DSN-403N (available from Daikin Industries, Ltd.).

Among these surfactants, FS-300 (available from E. I. du Pont de Nemoursand Company), FT-110, FT-250, FT-251, FT-400S, FT-150, and FT-400SW(available from NEOS COMPANY LIMITED), PolyFox PF-151N (available fromOMNOVA Solutions Inc.), and UNIDYNE™ DSN-403N (available from DaikinIndustries, Ltd.) are preferable since they can drastically improveprint quality, particularly color developing property, and permeability,wettability, and level dying property for paper.

The content rate of the surfactant in the ink is preferably in the rangeof from 0.001% to 5% by mass, more preferably from 0.05% to 5% by mass,from the aspects of wettability, discharge stability, and image quality,but is not limited thereto.

The ink may further include other additives, such as a pH adjuster, anantiseptic antifungal agent, an antirust, and a chelate reagent.

The pH adjuster is capable of keeping the ink alkaline to stabilize thedispersion state of the ink, thereby stabilizing discharge property ofthe ink. When the pH is 11 or above, inkjet heads and/or ink supplyunits may be dissolved out in large amounts, thereby causingalternation, leakage, and defective discharge of the ink after along-term use, depending on the material of the heads and/or units. Inpreparing the pigment dispersion, a pH adjuster is preferably kneadedwith or dispersed in water together with the pigment and a dispersant,rather than added together with other additives (e.g., a moisturizer, apenetrant) after the kneading or dispersing of the pigment with/inwater. This is because some pH adjusters may destroy a stabilizeddispersion state.

The pH adjuster preferably includes at least one of an alcohol amine, analkali metal hydroxide, an ammonium hydroxide, a phosphonium hydroxide,and an alkali metal carbonate.

Specific examples of the alcohol amine include, but are not limited to,diethanolamine, triethanolamine, and 2-amino-2-ethyl-1,3-propanediol.Specific examples of the alkali metal hydroxide include, but are notlimited to, lithium hydroxide, sodium hydroxide, and potassiumhydroxide. Specific examples of the ammonium hydroxide include, but arenot limited to, ammonium hydroxide and quaternary ammonium hydroxide.Specific examples of the phosphonium hydroxide include, but are notlimited to, quaternary phosphonium hydroxide. Specific examples of thealkali metal carbonate include, but are not limited to, lithiumcarbonate, sodium carbonate, and potassium carbonate.

Specific examples of the antiseptic antifungal agent include, but arenot limited to, sodium dehydroacetate, sodium sorbate,2-pyridinethio1-1-oxide sodium, sodium benzoate, and pentachlorophenolsodium.

Specific examples of the antirust include, but are not limited to, acidsulphite, sodium thiosul fate, ammonium thiodiglycolate,diisopropylammonium nitrite, pentaerythritol tetranitrate, anddicyclohexlyammonium nitrite.

Specific examples of the chelate reagent include, but are not limitedto, ethylenediaminetetraacetic acid tetrasodium salt, nitrilotriaceticacid trisodium salt, hydroxyethylethylenediaminetriacetic acid trisodiumsalt, diethylenetriaminepentaacetic acid pentasodium salt, anduramildiacetic acid disodium salt.

The ink is produced by dispersing or dissolving ink components,including optional components such as a penetrant and awater-dispersible resin, in an aqueous medium, and further stirring andmixing them, if needed. The dispersing may be performed by a sand mill,homogenizer, ball mill, paint shaker, ultrasonic disperser. The stirringand mixing may be performed by a stirrer equipped with stirring blades,magnetic stirrer, or high-speed disperser.

The ink is not limited in properties such as viscosity and surfacetension.

Preferably, the ink has a viscosity in the range of from 5 to 15 mPa·sat 25° C. When the ink viscosity is 5 mPa·s or more, print density andtext quality are improved. When the ink viscosity is 15 mPa·s or less,discharge stability is secured.

The viscosity can be measured by a viscometer (e.g., RE-550L availablefrom Toki Sangyo Co., Ltd.) at 25° C.

Preferably, the ink has a surface tension of 35 mN/m or less, morepreferably 32 mN/m or less, at 25° C. When the surface tension is 35mN/m or less, the leveling property of the ink on a recording medium isimproved.

The ink is not limited in color, and may have any color such as yellow,magenta, cyan, and black. An ink set including two or more inks havingdifferent colors can form multi-color images. An ink set including inkshaving yellow, magenta, cyan, and black colors can form full-colorimages.

The ink may be preferably used for a printer including an inkjet head ofany of the following types: a piezo type inkjet head in which apiezoelectric element, serving as a pressure generator for pressurizingink in an ink flow path, deforms a vibration plate founing a wallsurface of the ink flow path to vary the inner volume of the ink flowpath to discharge droplets of the ink (as described in Japanese ExaminedPatent Application Publication No. 02-51734, corresponding to JapaneseUnexamined Patent Application Publication No. 56-064877); a thermal typeinkjet head in which a heat element heats an ink in an ink flow path togenerate bubbles (as described in Japanese Examined Patent ApplicationPublication No. 61-59911, corresponding to Japanese Unexamined PatentApplication Publication No. 54-059936); and an electrostatic type inkjethead in which a vibration plate forming a wall surface of an ink flowpath and an electrode are facing each other and an electrostatic forcegenerated between the vibration plate and the electrode deforms thevibration plate to vary the inner volume of the ink flow path todischarge droplets of the ink (as described in Japanese UnexaminedPatent Application Publication No. 06-71882).

The ink may be preferably used for inkjet inks, ball-point pens,fountain pens, marker pens, and felt pens. In particular, the ink ispreferably used for inkjet image forming apparatuses (e.g., printers).As an example, the ink may be used for a printer in which a recordingmedium and an ink are heated to 50° C. to 200° C. at the time of, orimmediately before or after, printing of an image with the ink, toaccelerate fixing of the ink on the recording medium. The ink may alsobe used for an ink container, an inkjet recording apparatus, and an inkrecorded matter, as described below.

Recording Medium

As the recording medium, glossy coated papers composed of a photographicpaper base and a coated layer is preferably used. In addition, plainpapers having no coated layer are also preferably used. As an example,plain paper having a degree of sizing of 10 S or more and an airpermeability of from 5 to 50 S. which is generally used as copier paper,is preferable.

Ink Container

An ink container according to an embodiment of the present inventionincludes a container and the ink according to an embodiment of thepresent invention contained in the container, and optionally includesother members.

The container is not limited in shape, structure, size, and material.Examples of the container include, but are not limited to, an ink bagwhich is formed of an aluminum laminate film or a resin film.

Examples of the ink container include an ink cartridge. The inkcartridge is described in detail below with reference to FIGS. 1 and 2.

FIG. 1 is a schematic view of an ink bag 241. FIG. 2 is a schematic viewof an ink cartridge 200 including a cartridge casing 244 storing the inkbag 241.

Referring to FIG. 1, the ink bag 241 is filled with the ink through anink inlet 242. After the air remaining in the ink bag 241 is discharged,the ink inlet 242 is sealed by fusion.

When the ink bag 241 is put into use, an ink outlet 243, made of arubber material, is pricked with a needle of an apparatus body 101 ofand inkjet recording apparatus illustrated in FIG. 3 (to be describedlater), so that the ink can be supplied to the apparatus body 101.

The ink bag 241 may be formed of a wrapping material having no airpermeability, such as an aluminum laminate film.

Referring to FIG. 2, the ink bag 241 is stored in the cartridge casing244 made of a plastic material, thus providing the ink cartridge 200.The ink cartridge 200 can be detachably attachable to inkjet recordingapparatuses.

The ink cartridge 200 containing the ink is preferably detachablyattached to inkjet recording apparatuses.

Image Forming Method An image forming method according to an embodimentof the present invention includes the processes of applying a stimulusto the ink and flying the ink to a recording medium. The image formingmethod may further include the process of applying a treatment liquid tothe recording medium before and/or after the ink impacts on therecording medium, for the purpose of improving image quality such asimage density, strike-through resistance, and blurring resistance.

Ink Flying Process and Ink Flying Device

An ink flying process is a process in which a stimulus (i.e., energy) isapplied to the ink to fly the ink to a recording medium.

An ink flying device is a device which applies a stimulus (i.e., energy)to the ink to fly the ink to a recording medium. Specific examples ofthe ink flying device include, but are not limited to, ink dischargenozzles.

An inkjet head for discharging the ink may include a liquid chamber, afluid resistance part, a vibration plate, and a nozzle member. Theinkjet head is preferably made of a material containing silicon and/ornickel, at least in part.

The nozzle of the inkjet head preferably has a diameter of 30 μm orless, more preferably from 1 to 20 μm.

The stimulus (i.e., energy) may be generated by a stimulus generator.Specific examples of the stimulus include, but are not limited to, heat(temperature), pressure, vibration, and light. Each type of thesestimuli can be used alone or in combination with others. In particular,heat and pressure are preferable.

Examples of the stimulus generator include, but are not limited to, aheater, a presser, a piezoelectric element, a vibration generator, anultrasonic oscillator, and a light source. More specifically, thestimulus generator may be a piezoelectric actuator (e.g., piezoelectricelement); a thermal actuator using a thermoelectric conversion element,that uses phase change of a liquid caused by film boiling; ashape-memory alloy actuator using metal phase change caused bytemperature change; and an electrostatic actuator using electrostaticforce.

The ink flying process is not limited to any particular process. Whenthe stimulus is heat, one possible method includes giving thermal energywhich corresponds to a recording signal to the ink in a recording head,from a thermal head, to generate bubbles in the ink, thereby dischargingor injecting the ink droplets from nozzles of the recording head by thepressure of the bubbles. When the stimulus is pressure, one possiblemethod includes applying a voltage to a piezoelectric element attachedto a pressure chamber disposed in an ink flow path in a recording head,to make the piezoelectric element bend while reducing the volume of thepressure chamber, thereby discharging or injecting the ink droplets fromnozzles of the recording head.

The ink droplets preferably have a volume of from 3×10⁻¹⁵ to 40×10⁻¹⁵ m³(i.e., 3 to 40 pL). The discharge injection speed of the ink droplets ispreferably from 5 to 20 m/s. The drive frequency of the ink droplets ispreferably 1 kHz or more. The resolution of the ink droplets ispreferably 300 dpi or more.

An inkjet recording method according to an embodiment of the presentinvention may be performed with a serial type inkjet recording apparatusillustrated in FIG. 3 as described below. The inkjet recording apparatusillustrated in FIG. 3 includes: an apparatus body 101; a sheet feedingtray 102 to load sheets to the apparatus body 101; a sheet ejection tray103 to stack sheets having an image thereon; and an ink cartridgeloading unit 104. The ink cartridge loading unit 104 includes anoperation unit 105 on the upper surface thereof. The operation unit 105includes an operation key and a display. The ink cartridge loading unit104 further includes a front cover 115 that is openable and closable fordetaching/attaching an ink cartridge 201 therefrom/thereto.

Referring to FIGS. 4 and 5, the apparatus body 101 includes a guide rod131 horizontally bridging side plates, a stay 132, and a carriage 133.The guide rod 131 and the stay 132 slidably support the carriage 133 ina main scanning direction. A main scanning motor moves the carriage 133such that the carriage 133 scans in a carriage scanning direction shownby an arrow in FIG. 5.

The carriage 133 includes a recording head 134 that includes four inkjetheads for discharging droplets of yellow, cyan, magenta, and black inks,respectively. The inkjet heads each include multiple ink dischargenozzle arrays. The recording head 134 is mounted on the carriage 133with the multiple ink discharge nozzle arrays intersecting with the mainscanning direction and the ink droplet discharging direction coincidentwith a downward direction.

Each inkjet heads included in the recording head 134 may include anenergy generator for discharging ink, such as: a piezoelectric actuator(e.g., piezoelectric element); a thermal actuator using a thermoelectricconversion element, that uses phase change of a liquid caused by filmboiling; a shape-memory alloy actuator using metal phase change causedby temperature change; and an electrostatic actuator using electrostaticforce.

The carriage 133 further includes sub tanks 135 for supplying respectivecolor inks to the recording head 134. Each sub tank 135 is filled withthe ink, having been supplied from the ink cartridge 201 loaded on theink cartridge loading unit 104, through an ink supply tube.

The sheet feeding tray 102 includes a sheet stacker (pressure plate) 141stacking multiple sheets 142 thereon. The apparatus body 101 includes asheet feeder for feeding the sheets 142. The sheet feeder includes asheet feeding roller 143 having a semicircular shape and a separationpad 144 made of a material having a large friction coefficient. Thesheet feeding roller 143 separates and feeds the multiple sheets 142 oneby one. The separation pad 144 is disposed facing the sheet feedingroller 143 while being biased toward the sheet feeding roller 143.

The apparatus body 101 further includes a sheet conveyer for conveyingthe sheets 142 fed from the sheet feeder, at below the recording head134. The sheet conveyer includes a conveyance belt 151, a counter roller152, a conveyance guide 153, a pressing member 154, and a leading edgepressing roller 155. The conveyance belt 151 conveys each sheet 142while electrostatically adsorbing the sheet 142. The counter roller 152conveys the sheet 142 fed from the sheet feeder via a guide 145, whilesandwiching the sheet 142 with the conveyance belt 151. The conveyanceguide 153 changes the feed direction of the sheet 142 being fedsubstantially vertically upward by approximately 90 degrees, to make thesheet 142 follow the conveyance belt 151. The leading edge pressingroller 155 is biased toward the conveyance belt 151 by the pressingmember 154. The sheet conveyer further includes a charging roller 156for charging a surface of the conveyance belt 151.

The conveyance belt 151 is an endless belt stretched between aconveyance roller 157 and a tension roller 158. The conveyance belt 151is capable of circulating in a belt conveying direction. The conveyancebelt 151 includes a surface layer (i.e., sheet adsorbing surface) and aback layer (i.e., middle resistance layer, ground layer). The surfacelayer may include a resin material having a thickness of about 40 μmwithout resistance control, such as ethylene-tetrafluoroethylenecopolymer (ETFE). The back layer includes the same material as thesurface layer further including carbon black for resistance control. Onthe back side of the conveyance belt 151, a guide member 161 is disposedat a position corresponding to a printing area of the recording head134. The apparatus body 101 further includes a sheet ejector forejecting the sheets 142 having the image recorded by the recording head134 thereon. The sheet ejector includes a separation claw 171, a sheetejection roller 172, and another sheet ejection roller 173. Theseparation claw 171 separates the multiple sheets 142 one by one. Thesheet ejection tray 103 is disposed below the sheet ejection roller 172.

On the back surface side of the apparatus body 101, a duplex copy sheetfeeding unit 181 is detachably mounted. The duplex copy sheet feedingunit 181 incorporates the sheet 142 which has been returned by reverserotation of the conveyance belt 151, to reverse the sheet 142, and feedsthe reversed sheet 142 again to between the counter roller 152 and theconveyance belt 151. On the upper surface of the duplex copy sheetfeeding unit 181, a manual sheet feeder 182 is disposed.

The sheets 142 are separated by the sheet feeder one by one, and each ofthe sheets 142 is then fed substantially vertically upward while beingguided by the guide 14, and sandwiched between the conveyance belt 151and the counter roller 152. The leading edge of the sheet 142 is guidedby the conveyance guide 153 and pressed against the conveyance belt 151with the leading edge pressing roller 155. Thus, the conveyancedirection of the sheet 142 is changed by approximately 90 degrees.

At this time, the conveyance belt 151 has been charged by the chargingroller 156. The sheet 142 is conveyed by the conveyance belt 151 whilebeing electrostatically adsorbed thereto. The recording head 134 isdriven to discharge ink droplets according to an image signal, while thecarriage 133 is being moved and the sheet 142 is being stopped, thusrecoding one line of an image on the sheet 142. The sheet 142 isconveyed for a predetermined amount thereafter and the next recordingoperation is performed. In response to receiving a recording end signalor another signal indicating that the trailing edge of the sheet 142 hasreached the recording area, the recording operation is finished and thesheet 142 is ejected on the sheet ejection tray 103.

In response to a near end detection of the ink remaining in the sub tank135, a required amount of the ink is supplied to the sub tank 135 fromthe ink cartridge 201.

When the inkjet recording apparatus runs out of the ink in the inkcartridge 201, the casing of the ink cartridge 201 may be disassembledso that the ink bag 241 inside the ink cartridge 201 can be replaced.Although being placed vertically and loaded to the front face of theapparatus body 101, the ink cartridge 201 reliably supplies the inks.Thus, even in a case in which the upper surface of the apparatus body101 is covered, for example, in a case in which the apparatus body 101is stored in a rack or something is put on the upper surface of theapparatus body 101, the ink cartridge 201 is easily replaceable.

The inkjet recording apparatus according to some embodiments of thepresent invention may be either a serial (shuttle) type inkjet recordingapparatus equipped with a carriage to scan, as described above, or aline type inkjet recording apparatus equipped with a line head.

The inkjet recording apparatus and inkjet recording method according tosome embodiments of the present invention can be applied to variousapparatuses, such as inkjet printers, facsimile machines, copiers, andmultifunctional peripherals (having the functions of printer, facsimilemachine, and copier).

Inkjet Recorded Matter

An ink recorded matter according to an embodiment of the presentinvention is recorded by the above-described inkjet recording apparatus.

The ink recorded matter includes a recording medium and an image formedwith the ink on the recording medium.

Specific examples of the recording medium include, but arc not limitedto, plain paper, glossy paper, and general-purpose printing paper. Eachtype of these recording media can be used alone or in combination withothers.

The ink recorded matter has high image quality without blurring andexcellent temporal stability. The ink recorded matter can be used forvarious purposes such as a material for recording texts and/or images.

EXAMPLES

Having generally described this invention, further understanding can beobtained by reference to certain specific examples which are providedherein for the purpose of illustration only and are not intended to belimiting. In the descriptions in the following examples, the numbersrepresent mass ratios in parts, unless otherwise specified.

Preparation Example 1 Preparation of Magenta-Pigment-Containing PolymerParticle Dispersion Liquid Preparation of Polymer Solution A

After sufficiently replacing the air in a 1-L flask, equipped with amechanical stirrer, a thermometer, a nitrogen gas inlet pipe, a refluxpipe, and a dropping funnel, with nitrogen gas, 11.2 g of styrene, 2.8 gof acrylic acid, 12.0 g of lauryl methacrylate, 4.0 g of polyethyleneglycol methacrylate, 4.0 g of styrene macromer, and 0.4 g ofmercaptoethanol were mixed in the flask and heated to 65° C.

Next, a mixture liquid containing 100.8 g of styrene, 25.2 g of acrylicacid, 108.0 g oflauryl methacrylate, 36.0 g of polyethylene glycolmethacrylate, 60.0 g of hydroxyethyl methacrylate, 36.0 g of styrenemacromer, 3.6 g of mercaptoethanol, 2.4 g of azobis methylvaleronitrile,and 18 g of methyl ethyl ketone was dropped in the flask over a periodof 2.5 hours. Next, another mixture liquid containing 0.8 g of azobismethylvaleronitrile and 18 g of methyl ethyl ketone was further droppedin the flask over a period of 0.5 hours. After aging the mixture at 65°C. for 1 hour, 0.8 g of azobis methylvaleronitrile was added thereto,and the mixture was further aged for 1 hour. After completion of thereaction, 364 g of methyl ethyl ketone was added to the flask. Thus, 800g a polymer solution A having a concentration of 50% was obtained.

Preparation of Pigment-Containing Polymer Particle Dispersion Liquid

First, 28 g of the polymer solution A, 42 g of C.I. Pigment Red 122,13.6 g of a 1-mol/L aqueous solution of potassium hydroxide, 20 g ofmethyl ethyl ketone, and 13.6 g of ion-exchange water were sufficientlymixed and stirred. The resulting mixture was kneaded with a roll mill.The resulting paste was poured in 200 g of pure water and sufficientlystifled, and methyl ethyl ketone and water were evaporated therefromusing an evaporator. The resulting dispersion liquid was subjected topressure filtration using a polyvinylidene fluoride membrane filterhaving an average pore diameter of 5.0 μm to remove coarse particles.Thus, a magenta-pigment-containing polymer particle dispersion liquidcontaining 15% by mass of the pigment and 20% by mass of solid contentswas prepared. The average particle diameter (D50) of the polymerparticle contained in the magenta-pigment-containing polymer particledispersion liquid was 82.7 nm. The average particle diameter (D50) wasmeasured with a particle size distribution analyzer (NANOTRAC UPA-EX150available from Nikkiso Co., Ltd.).

Preparation Example 2 Preparation of Cyan-Pigment-Containing PolymerParticle Dispersion Liquid

The procedure in Preparation Example 1 was repeated except for replacingthe magenta pigment C.I. Pigment Red 122 with a phthalocyanine pigment(C.I. Pigment Blue 15:3). Thus, a cyan-pigment-containing polymerparticle dispersion liquid was prepared.

The particle diameter (D50) of the polymer particle contained in thecyan-pigment-containing polymer particle dispersion liquid measured by aparticle size distribution analyzer (NANOTRAC UPA-EX150 available fromNikkiso Co., Ltd.) was 110.6 nm.

Preparation Example 3 Preparation of Yellow-Pigment-Containing PolymerParticle Dispersion Liquid

The procedure in Preparation Example 1 was repeated except for replacingthe magenta pigment C.I. Pigment Red 122 with a monoazo yellow pigment(C.I. Pigment Yellow 74). Thus, a yellow-pigment-containing polymerparticle dispersion liquid was prepared.

The particle diameter (D50) of the polymer particle contained in theyellow-pigment-containing polymer particle dispersion liquid measured bya particle size distribution analyzer (NANOTRAC UPA-EX150 available fromNikkiso Co., Ltd.) was 105.4 nm.

Preparation Example 4 Preparation of Carbon-Black-Pigment-ContainingPolymer Particle Dispersion Liquid

The procedure in Preparation Example 1 was repeated except for replacingthe magenta pigment C.I. Pigment Red 122 with a carbon black (FW100available from Degussa). Thus, a carbon-black-pigment-containing polymerparticle dispersion liquid was prepared.

The particle diameter (D50) of the polymer particle contained in thecarbon-black-pigment-containing polymer particle dispersion liquidmeasured by a particle size distribution analyzer (NANOTRAC UPA-EX150available from Nikkiso Co., Ltd.) was 75.2 nm.

Preparation Example 5

First, 200 parts of a carbon black (NIPEX 150 available from Deggusa,having a BET specific surface area of 110 m²/g, an average primaryparticle diameter of 29 nm, a pH of 4.0, and a DBP oil absorption of 400g/100 g), 12.5 parts of a sodium naphthalenesulfonate formalincondensate (PAIONIN A-45-PN available from Takemoto Oil & Fat Co., Ltd.,the total content of dimer, trimer, and tetramer of naphthalenesulfonicacid being 30% by mass), and 788 parts of distilled water were premixed.Thus, a mixture slurry was prepared. The mixture slurry was subjected toa circulation dispersion using a disc-type media mill (MSC millavailable from Nippon Coke & Engineering Co., Ltd.) filled with zirconiabeads having a diameter of 0.015 mm with a filing ratio of 70% at aperipheral speed of 8 m/s and a liquid temperature of 10° C. for 3minutes. The mixture slurry was then subjected to a centrifugalseparation using a centrifugal separator (MODEL-7700 available fromKUBOTA Corporation) to remove coarse particles. Thus, a black pigmentdispersion 1 was prepared. The particle diameter (D50) of the blackpigment dispersion 1 measured by a particle size distribution analyzer(MICROTRAC UPA available from Nikkiso Co., Ltd.) was 125 nm.

Preparation Example 6

Preparation of Acrylic Silicone Resin Particle Aqueous Dispersion 1After sufficiently replacing the air in a 1-L flask, equipped with amechanical stirrer, a thermometer, a nitrogen gas inlet pipe, a refluxpipe, and a dropping funnel, with nitrogen gas, 17.5 g of LATEMUL S-180(available from Kao Corporation) and 350 g of ion-exchange water weremixed in the flask and heated to 65° C.

After the heating, 3.0 g of t-butyl peroxybenzoate (serving as areaction initiator) and 1.0 g of sodium isoascorbate were added to theflask. Five minutes later, a mixture of 45 g of methyl methacrylate, 160g of 2-etyhylhexyl methacrylate, 5 g of acrylic acid, 45 g of butylmethacrylate, 30 g of cyclohexyl methacrylate, 15 g of vinyltriethoxysilane, 8.0 g of LATEMUL S-180 (available from KaoCorporation), and 340 g of ion-exchange water was dropped in the flaskover a period of 3 hours.

The flask contents were aged at 80° C. for 2 hours and then cooled tonormal temperature. The pH thereof was adjusted to 7 to 8 using sodiumhydroxide.

Ethanol was removed using an evaporator, and the moisture content wascontrolled. Thus, 730 g of an acrylic silicone resin particle aqueousdispersion 1 containing 40% by mass of solid contents was prepared. Theparticle diameter (D50) of the acrylic silicone resin particle aqueousdispersion 1 measured by a particle size distribution analyzer (NANOTRACUPA-EX150 available from Nikkiso Co., Ltd.) was 35 nm.

Preparation Example 7 Preparation of Polyurethane Resin Particle AqueousDispersion 1

A simple pressure reactor equipped with a stirrer and a heater wascharged with 287.9 g of a crystalline polycarbonate diol (DURANOL™ T6002available from Asahi Kasei Chemicals Corp.) having a number averagemolecular weight (Mn) of 2,000, 3.6 g of 1,4-butanediol, 8.9 g of DMPA(dimethylol propionic acid), 98.3 g of hydrogenated MDI, and 326.2 partsof acetone while introducing nitrogen thereto.

The contents were heated to 90° C. and subjected to an urethane-formingreaction over a period of 8 hours to produce a prepolymer. The reactionproduct mixture was cooled to 40° C. and mixed with 10.0 g oftriethylamine. The mixture was further mixed with 568.8 g of water, andemulsification was caused by a rotor-stator-type mechanical emulsifier.Thus, an aqueous dispersion was prepared. Next, 28.1 g of a 10% aqueoussolution of ethylenediamine was added to the above-obtained aqueousdispersion being stirred. The aqueous dispersion was further stirred for5 hours at 50° C. to cause a chain elongation reaction.

Acetone was removed from the aqueous dispersion under reduced pressureat 65° C., and the moisture content was controlled. Thus, a polyurethaneresin particle aqueous dispersion 1 containing 40% by mass of solidcontents was prepared. The particle diameter (D50) of the polyurethaneresin particle aqueous dispersion 1 measured by a particle sizedistribution analyzer (NANOTRAC UPA-EX150 available from Nikkiso Co.,Ltd.) was 9 nm.

Preparation Example 8

Preparation of Polyurethane Resin Particle Aqueous Dispersion 2 Theprocedure in Preparation Example 7 was repeated except for changing theaddition amount of triethylamine to 6.8 g. Thus, a polyurethane resinparticle aqueous dispersion 2 was prepared. The particle diameter (D50)of the polyurethane resin particle aqueous dispersion 2 measured by aparticle size distribution analyzer (NANOTRAC UPA-EX150 available fromNikkiso Co., Ltd.) was 25 nm.

Preparation Example 9

Preparation of Polyurethane Resin Particle Aqueous Dispersion 3 Theprocedure in Preparation Example 7 was repeated except for changing theaddition amount of triethylamine to 3.9 g. Thus, a polyurethane resinparticle aqueous dispersion 3 was prepared. The particle diameter (D50)of the polyurethane resin particle aqueous dispersion 3 measured by aparticle size distribution analyzer (NANOTRAC UPA-EX150 available fromNikkiso Co., Ltd.) was 95 nm.

Examples 1-19 and Comparative Examples 1-13

Preparation of Inkjet Inks Each inkjet ink was prepared as follows.

According to the fonnulations described in Tables 1-1 and 1-2, first,organic solvents, surfactants, and water were uniformly stirred andmixed for one hour. Next, each resin particle dispersion liquid wasadded to each mixture and stirred for one hour, and then each pigmentdispersion liquids was added to each mixture and stirred for one hour.Each of the resulting dispersion liquids was subjected to a pressurefiltration using a polyvinylidene fluoride membrane filter having anaverage pore diameter of 5.0 μm to remove coarse particles and foreignsubstances. Thus, inks of Examples 1-19 and Comparative Examples 1-13were prepared. In addition to the contents listed in Tables 1-1 and 1-2,a penetrant, an antifungal agent, a defoamer, and a pH adjuster wereadded to each ink.

TABLE 1-1 D50 Examples (nm) 1 2 3 4 5 6 7 8 9 10 PigmentMagenta-pigment- Dispersion containing Polymer Liquids ParticleDispersion (as Pigment Liquid (Preparation Solid Example 1) Contents)Cyan-pigment- containing Polymer Particle Dispersion Liquid (PreparationExample 2) Yellow-pigment- containing Polymer Particle Dispersion Liquid(Preparation Example 3) Black-pigment- containing Polymer ParticleDispersion Liquid (Preparation Example 4) Black Pigment Dispersion(Preparation Example 5) Self-dispersible Magenta Pigment DispersionLiquid (CAB-O-JET 260) Self-dispersible Cyan Pigment Dispersion Liquid(CAB-O-JET 250) Self-dispersible Yellow Pigment Dispersion Liquid(CAB-O-JET 270) Self-dispersible 8 8 8 8 8 8 8 8 8 8 Black PigmentDispersion Liquid (CAB-O-JET 300) Resin Acrylic Silicone 35 ParticleResin Particle Dispersion Aqueous Dispersion Liquids (Preparation (asSolid Example 6) Contents) Polyurethane Resin 9 Particle AqueousDispersion 1 (Preparation Example 7) Polyurethane Resin 25 2 ParticleAqueous Dispersion 2 (Preparation Example 8) Polyurethane Resin 95Particle Aqueous Dispersion 3 (Preparation Example 9) Urethane Resin 352 UA-3945 Urethane Resin 17 2 2 2 2 2 2 1 3 UWS-145 Urethane Resin 160APX-101 Organic 3-Methoxy-1- 2 2 1 8 10 12 2 1 Solvents butanol3-Methoxy-1- 2 8 propanol Glycerin 14 13 14 15 7 8 5 4 13 121,2-Butanediol 1,3-Butanediol 10 10 10 10 10 10 10 10 10 103-Methyl-1,3- 10 10 10 10 10 10 10 10 10 10 butanediol SurfactantsDSN403N 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 0.10 EP7025 0.50 PureWater Residue Residue Residue Residue Residue Residue Residue ResidueResidue Residue Total 100 100 100 100 100 100 100 100 100 100 SolventQuantity 36.1 35.5 36.1 36.1 35.1 36.1 35.1 36.1 35.1 33.1Solvents/Resin Ratio 1.0 1.0 1.0 0.5 4.0 4.0 5.0 6.0 2.0 0.3 Viscosity(mPa · s) 7.8 8.0 8.2 8.3 7.8 7.8 8.0 8.0 8.3 7.8 Change in Viscosity(%) 0.5 −0.5 0.7 −1.0 1.8 2.0 4.0 5.5 0.1 −1.1 (Storage Stability) RubResistance 1: Image A A A A A A A A A A Peel-off Rub Resistance 2:Fouling A A A A A A A A A A in Non-printed Part Discharge Stability A AA A A A B B A A D50 Examples (nm) 11 12 13 14 15 16 17 18 19 PigmentMagenta-pigment- 7 Dispersion containing Polymer Liquids ParticleDispersion (as Pigment Liquid (Preparation Solid Example 1) Contents)Cyan-pigment- 5 containing Polymer Particle Dispersion Liquid(Preparation Example 2) Yellow-pigment- 5 containing Polymer ParticleDispersion Liquid (Preparation Example 3) Black-pigment- 8 containingPolymer Particle Dispersion Liquid (Preparation Example 4) Black Pigment8 Dispersion (Preparation Example 5) Self-dispersible 7 Magenta PigmentDispersion Liquid (CAB-O-JET 260) Self-dispersible 5 Cyan PigmentDispersion Liquid (CAB-O-JET 250) Self-dispersible 5 Yellow PigmentDispersion Liquid (CAB-O-JET 270) Self-dispersible 8 Black PigmentDispersion Liquid (CAB-O-JET 300) Resin Acrylic Silicone 35 ParticleResin Particle Dispersion Aqueous Dispersion Liquids (Preparation (asSolid Example 6) Contents) Polyurethane Resin 9 Particle AqueousDispersion 1 (Preparation Example 7) Polyurethane Resin 25 2 1 2 3Particle Aqueous Dispersion 2 (Preparation Example 8) Polyurethane Resin95 Particle Aqueous Dispersion 3 (Preparation Example 9) Urethane Resin35 2 UA-3945 Urethane Resin 17 3 2 3 2 UWS-145 Urethane Resin 160APX-101 Organic 3-Methoxy-1- 2 2 2 2 1 Solvents butanol 3-Methoxy-1- 2 22 2 1 propanol Glycerin 14 13 13 14 8 13 14 8 14 1,2-Butanediol1,3-Butanediol 15 11 10 10 10 10 10 10 10 3-Methyl-1,3- 10 10 10 10 1010 10 10 10 butanediol Surfactants DSN403N 0.10 0.10 0.10 0.10 0.10 0.100.10 0.10 EP7025 0.50 Pure Water Residue Residue Residue Residue ResidueResidue Residue Residue Residue Total 100 100 100 100 100 100 100 100100 Solvent Quantity 41.5 36.1 35.1 36.1 30.1 35.1 36.1 30.1 36.1Solvents/Resin Ratio 1.0 0.7 2.0 1.0 1.0 0.7 0.7 1.0 1.0 Viscosity (mPa· s) 8.0 7.8 8.3 8.0 8.0 8.0 8.0 8.0 7.9 Change in Viscosity (%) 0.5 0.2−0.5 −1.0 0.5 −1.1 1.0 2.5 0.3 (Storage Stability) Rub Resistance 1:Image A A A A A A A A A Peel-off Rub Resistance 2: Fouling A A A A A A AA A in Non-printed Part Discharge Stability A A A A A A A A A

TABLE 1-2 D50 Comparative Examples (nm) 1 2 3 4 5 6 7 PigmentMagenta-pigment-containing Polymer Particle Dispersion Dispersion Liquid(Preparation Example 1) Liquids Cyan-pigment-containing Polymer Particle(as Pigment Dispersion Liquid (Preparation Example 2) SolidYellow-pigment-containing Polymer Particle Contents) Dispersion Liquid(Preparation Example 3) Black-pigment-containing Polymer ParticleDispersion Liquid (Preparation Example 4) Black Pigment Dispersion 8(Preparation Example 5) Self-dispersible Magenta Pigment 7 DispersionLiquid (CAB-O-JET 260) Self-dispersible Cyan Pigment 5 Dispersion Liquid(CAB-O-JET 250) Self-dispersible Yellow Pigment Dispersion Liquid(CAB-O-JET 270) Self-dispersible Black Pigment 8 8 8 8 Dispersion Liquid(CAB-O-JET 300) Resin Acrylic Silicone Resin Particle 35 2 ParticleAqueous Dispersion (Preparation Example 6) Dispersion Polyurethane ResinParticle 9 Liquids Aqueous Dispersion 1 (Preparation Example 7) (asSolid Polyurethane Resin Particle 25 2 4 1 Contents) Aqueous Dispersion2 (Preparation Example 8) Polyurethane Resin Particle 95 AqueousDispersion 3 (Preparation Example 9) Urethane Resin UA-3945 35 2Urethane Resin UWS-145 17 2 2 1 Urethane Resin APX-101 160 Organic3-Methoxy-1-butanol Solvents 3-Methoxy-1-propanol Glycerin 15 15 15 1515 15 16 1,2-Butanediol 11 1,3-Butanediol 10 15 15 15 15 15 103-Methyl-1,3-butanediol 5 5 5 8 7 10 Surfactants DSN403N 0.10 0.10 0.100.10 0.10 0.10 EP7025 0.50 Pure Water Residue Residue Residue ResidueResidue Residue Residue Total 100 100 100 100 100 100 100 SolventQuantity 36.1 35.5 35.1 35.1 38.1 37.1 36.1 Solvents/Resin Ratio — 0.00.0 0.0 0.0 0.0 0.0 Viscosity (mPa · s) 8.0 8.1 8.1 7.2 8.0 8.0 8.0Change in Viscosity (%) (Storage Stability) 1.0 2.0 −18.0 −8.0 −12.0−16.2 −12.1 Rub Resistance 1: Image Peel-off C B A A A A A RubResistance 2: Fouling in Non-printed Part C A A A A A A DischargeStability A A A A A A A D50 Comparative Examples (nm) 8 9 10 11 12 13Pigment Magenta-pigment-containing Polymer Particle DispersionDispersion Liquid (Preparation Example 1) LiquidsCyan-pigment-containing Polymer Particle 5 (as Pigment Dispersion Liquid(Preparation Example 2) Solid Yellow-pigment-containing Polymer Particle5 Contents) Dispersion Liquid (Preparation Example 3)Black-pigment-containing Polymer Particle 8 Dispersion Liquid(Preparation Example 4) Black Pigment Dispersion (Preparation Example 5)Self-dispersible Magenta Pigment Dispersion Liquid (CAB-O-JET 260)Self-dispersible Cyan Pigment Dispersion Liquid (CAB-O-JET 250)Self-dispersible Yellow Pigment Dispersion Liquid (CAB-O-JET 270)Self-dispersible Black Pigment 8 8 8 Dispersion Liquid (CAB-O-JET 300)Resin Acrylic Silicone Resin Particle 35 Particle Aqueous Dispersion(Preparation Example 6) Dispersion Polyurethane Resin Particle 9 2Liquids Aqueous Dispersion 1 (Preparation Example 7) (as SolidPolyurethane Resin Particle 25 2 3 Contents) Aqueous Dispersion 2(Preparation Example 8) Polyurethane Resin Particle 95 2 AqueousDispersion 3 (Preparation Example 9) Urethane Resin UA-3945 35 UrethaneResin UWS-145 17 3 Urethane Resin APX-101 160 2 Organic3-Methoxy-1-butanol Solvents 3-Methoxy-1-propanol Glycerin 10 16 16 1015 15 1,2-Butanediol 1,3-Butanediol 10 10 10 10 10 103-Methyl-1,3-butanediol 10 9 9.5 10 10 10 Surfactants DSN403N 0.10 0.100.10 0.10 0.10 0.10 EP7025 Pure Water Residue Residue Residue ResidueResidue Residue Total 100 100 100 100 100 100 Solvent Quantity 30.1 35.135.6 30.1 35.1 35.1 Solvents/Resin Ratio 0.0 0.0 0.0 0.0 0.0 0.0Viscosity (mPa · s) 8.0 8.0 8.0 8.0 10.5 8.1 Change in Viscosity (%)(Storage Stability) −9.2 −20.5 −18.2 2.8 0.5 2.2 Rub Resistance 1: ImagePeel-off A A A C C C Rub Resistance 2: Fouling in Non-printed Part A A AC C C Discharge Stability A A A A A A

Abbreviations listed in Tables 1-1 and 1-2 represent the followingcompounds.

Pigment Dispersion Liquids

-   CAB-O-JET 260: A self-dispersible magenta pigment dispersion liquid    containing 11% of pigment solid contents, available from Cabot    Corporation.-   CAB-O-JET 250: A self-dispersible cyan pigment dispersion liquid    containing 11% of pigment solid contents, available from Cabot    Corporation.-   CAB-O-JET 270: A self-dispersible yellow pigment dispersion liquid    containing 11% of pigment solid contents, available from Cabot    Corporation.-   CAB-O-JET 300: A self-dispersible black pigment dispersion liquid    containing 15% of pigment solid contents, available from Cabot    Corporation.    Resin Particle Dispersion Liquids-   Urethane Resin UA-3945: An urethane resin particle dispersion liquid    UCOAT UA-3945 available from Sanyo Chemical industries, Ltd.,    containing 38.4% by mass of solid contents and having an average    particle diameter of 35 m.-   Urethane Resin UWS-145: An urethane resin particle dispersion liquid    UCOAT UWS-145 available from Sanyo Chemical industries, Ltd.,    containing 35.0% by mass of solid contents and having an average    particle diameter of 17 nm.-   Urethane Resin APX-101: An urethane resin particle dispersion liquid    HYDRAN APX-101H available from DIC Corporation, containing 45% by    mass of solid contents and having an average particle diameter of    160 nm and a minimum film forming temperature (MFT) of 20° C.    Surfactants-   DSN403N: A fluorosurfactant DSN403N available from Daikin    Industries, Ltd., containing 98% by mass or more of active    ingredients. EP-7025: A polyoxyalkylene alkyl ether SOFTANOL EP-7025    available from NIPPON SHOKUBAI CO., LTD., containing 100% by mass of    active ingredients.    Evaluation Items    Ink Properties    Viscosity of Ink

Viscosity of each ink was measured with a viscometer (RE-550L availablefrom Toki Sangyo Co., Ltd.) at 25° C.

pH of Ink

pH of each ink was measured with a pH meter (HM-30R available fromDKK-TOA Corporation) at 25° C.

Particle Diameter (D50)

Each ink was diluted with pure water such that the solid contentconcentration became 0.01% by mass. A particle diameter (D50) of thepigment in each ink was measured with a particle size distributionanalyzer (NANOTRAC UPA-EX150 available from Nikkiso Co., Ltd.).

Storage Stability of Ink

Each ink was sealed in a polyethylene container and stored at 70° C. for1 week. Before and after the storage, each ink was subjected to themeasurement of viscosity. The rate of change in viscosity before andafter the storage was determined by the following formula 1, and storagestability of the ink was evaluated according to the following evaluationcriteria.

$\begin{matrix}{{{Change}\mspace{14mu}{in}\mspace{14mu}{{Viscosity}(\%)}} = {\frac{\begin{pmatrix}{\left( {{Ink}\mspace{14mu}{Viscosity}\mspace{14mu}{After}\mspace{14mu}{Storage}} \right) -} \\\left( {{Ink}\mspace{14mu}{Viscosity}\mspace{14mu}{Before}\mspace{14mu}{Storage}} \right)\end{pmatrix}}{\left( {{Ink}\mspace{14mu}{Viscosity}\mspace{14mu}{Before}\mspace{14mu}{Storage}} \right)} \times 100}} & \left( {{Formula}\mspace{14mu} 1} \right)\end{matrix}$

Evaluation Criteria

-   -   A: The rate of change in viscosity was less than 4%.    -   B: The rate of change in viscosity was 4% or more and less than        8%.    -   C: The rate of change in viscosity was 8% or more.        Image Formation

Each ink was mounted on an inkjet recording apparatus (IPSiO GXe-5500available from Ricoh Co., Ltd.). The drive voltage of the piezo elementin this inkjet recording apparatus was changed such that the dischargeamount of ink become constant and the deposited amount of the ink on arecording medium become constant, under an environmental condition of23±0.5° C., 50±5% RH. The inkjet recording apparatus was allowed toprint image while setting the printing mode to “Plain paper/Fast” or“Glossy paper/Slow”.

Rub Resistance 1: Image Peel-off

A solid image chart with each side having a length of 3 cm was printedon a sheet of a glossy paper POSTER PAPER MAX available from SakuraiCo., Ltd. having a basis weight of 180 g/m² while setting the printingmode to “Glossy paper/Fast”.

After being dried, the printed part was rubbed with cotton cloth backand forth 5 times. The printed part was then visually observed to checkwhether image peel-off had occurred or not. Rub resistance 1 wasevaluated based on the following criteria.

Evaluation Criteria

-   -   A: No image peel-off was observed.    -   B: Slight image peel-off was observed at the end parts of the        image.    -   C: Image peel-off was observed.        Rub Resistance 2: Fouling in Non-printed Part

A solid image chart with each side having a length of 3 cm was printedon a sheet of a glossy paper POSTER PAPER MAX available from SakuraiCo., Ltd. having a basis weight of 180 g/m² while setting the printingmode to “Glossy paper/Fast”.

After being dried, the printed part was rubbed with cotton cloth backand forth 5 times. The non-printed part was then visually observed tocheck whether image stretching or fouling (caused by image transfer) hadoccurred or not. Rub resistance 2 was evaluated based on the followingcriteria.

Evaluation Criteria

-   -   A: No fouling was observed.    -   B: Slight fouling was observed.    -   C: Fouling was observed.        Discharge Stability

An A4-size chart including solid parts having an area ratio of 5% percolor, formed with MICROSOFT WORD 2000, was continuously printed on 200sheets of MY PAPER (available from Ricoh Co., Ltd.). Discharge stabilitywas evaluated based on the degree of disturbance in discharge at eachnozzle after the continuous printing. The printing mode “Plainpaper/Standard/Fast” was modified to “No color correction” through theuser setting for plain paper using a driver attached to the printer.

Evaluation Criteria

-   -   A: Disturbance in discharge was not observed.    -   B: Disturbance in discharge was slightly observed.    -   C: Disturbance in discharge was observed, or discharge was not        performed in part.

The evaluation results for Examples 1-19 and Comparative Examples 1-13are shown in Table 2.

TABLE 2 Resin Storage Stability Rub Resistance Solvent Particle Changein Fouling in Amount Diameter Solvent/Resin Viscosity ViscosityEvaluation Image Non-printed Discharge (%) (nm) Ratio (mPa · s) (%)Result Peel-off Part Stability Example 1 36.1 35 1.0 7.8 0.5 A A A AExample 2 35.5 17 1.0 8.0 −0.5 A A A A Example 3 36.1 25 1.0 8.2 0.7 A AA A Example 4 36.1 17 0.5 8.3 −1.0 A A A A Example 5 35.1 17 4.0 7.8 1.8A A A A Example 6 36.1 17 4.0 7.8 2.0 A A A A Example 7 36.1 17 5.0 8.04.0 A A A B Example 8 36.1 17 6.0 8.0 5.5 B A A B Example 9 35.1 17 2.08.3 0.1 A A A A Example 10 33.1 17 0.3 7.8 −1.1 A A A A Example 11 41.525 1.0 8.0 0.5 A A A A Example 12 36.1 17 0.7 7.8 0.2 A A A A Example 1335.1 25 2.0 8.3 −0.5 A A A A Example 14 36.1 17 1.0 8.0 −1.0 A A A AExample 15 30.1 25 1.0 8.0 0.5 A A A A Example 16 35.1 17 0.7 8.0 −1.1 AA A A Example 17 36.1 25 0.7 8.0 1.0 A A A A Example 18 30.1 17 1.0 8.02.5 A A A A Example 19 36.1 35 1.0 7.9 0.3 A A A A Comparative Example 136.1 — — 8.0 1.0 A C C A Comparative Example 2 35.5 35 0.0 8.1 2.0 A B AA Comparative Example 3 35.1 17 0.0 8.1 −18.0 C A A A ComparativeExample 4 35.1 25 0.0 7.2 −8.0 C A A A Comparative Example 5 38.1 25 0.08.0 −12.0 C A A A Comparative Example 6 37.1 17 0.0 8.0 −16.2 C A A AComparative Example 7 36.1 25 0.0 8.0 −12.1 C A A A Comparative Example8 30.1 25 0.0 8.0 −9.2 C A A A Comparative Example 9 35.1 17 0.0 8.0−20.5 C A A A Comparative Example 10 35.6 25 0.0 8.0 −18.2 C A A AComparative Example 11 30.1 95 0.0 8.0 2.8 A C C A Comparative Example12 35.1 9 0.0 10.5 0.5 A C C A Comparative Example 13 35.1 160 0.0 8.12.2 A C C A

Numerous additional modifications and variations are possible in lightof the above teachings. It is therefore to be understood that, withinthe scope of the above teachings, the present disclosure may bepracticed otherwise than as specifically described herein. With someembodiments having thus been described, it will be obvious that the samemay be varied in many ways. Such variations are not to be regarded as adeparture from the scope of the present disclosure and appended claims,and all such modifications are intended to be included within the scopeof the present disclosure and appended claims.

What is claimed is:
 1. An ink, comprising: an organic solvent comprisingat least one of 3-methoxy-1-butanol and 3-methoxy-1-propanol; a pigment;a polyurethane particle having a particle diameter D50 of 50 nm or less;and water, wherein a mass ratio of the at least one of3-methoxy-1-butanol and 3-methoxy-1-propanol to the polyurethaneparticle ranges from 0.2 to 5.0.
 2. The ink of claim 1, wherein theparticle diameter D50 ranges from 10 to 30 nm.
 3. The ink of claim 1,wherein the at least one of 3-methoxy-1-butanol and 3-methoxy-1-propanolaccounts for 0.8% to 12% by mass of the ink.
 4. The ink of claim 1,wherein the mass ratio of the at least one of 3-methoxy-1-butanol and3-methoxy-1-propanol to the polyurethane particle ranges from 0.5 to4.0.
 5. An ink container comprising: a container; and the ink of claim 1contained in the container.
 6. An inkjet recording apparatus comprising:the ink container of claim 5; and a recording head to discharge the ink.7. The ink of claim 1, wherein the particle diameter D50 ranges from 10to 30 nm and wherein the organic solvent comprises 3-methoxy-1-butanol.8. The ink of claim 1, wherein the particle diameter D50 ranges from 10to 30 nm and wherein the organic solvent comprises 3-methoxy-1-propanol.9. The ink of claim 1, wherein the organic solvent comprises3-methoxy-1-butanol and 3-methoxy-1-propanol.
 10. The ink of claim 1,wherein organic solvent comprises 3-methoxy-1-butanol.
 11. The ink ofclaim 1, wherein the organic solvent comprises 3-methoxy-1-propanol. 12.The ink of claim 1, wherein the ink is a yellow, magenta, or cyan ink.